Our mammalian friends won’t be heading into fin-to-fin combat anytime soon, though. As the Guardian explains, they’re mostly used to find underwater mines:
Yes, the navy trains and keeps dolphins, whose powerful innate echolocation abilities help sailors spot suspicious undersea objects that might be mines. The marine mammal enlistees are the aquatic equivalent of the dogs, whose sophisticated sense of smell has aided US soldiers in the hunt for homemade insurgent bombs on land.
The Russian paper Izvestia recently reported that the U.S. deployed a dolphin squad to waters near Ukraine, a claim the Navy flatly denies: “There is no truth to this report,” said Lieutenant Commander Katie Cerezo.